Conventional semi-monocoque panels used in aircraft fuselages typically include a plurality of longitudinal stiffeners or stringers attached to an inner surface of a skin. Circumferential frames extending transverse to the stringers are typically attached to the inner surface of the skin at longitudinally spaced-apart intervals to give the fuselage its cross-sectional shape. The frames often include openings or “mouse holes” through which the stringers extend, and the panel often includes a plurality of small clips or shear ties fastening the frames to the stringers at the mouse holes. While such panels can be relatively strong and lightweight, conventional methods for manufacturing such panels are typically labor-intensive because of the number of parts that must be assembled.
FIG. 1 is an isometric view of a semi-monocoque aircraft panel 100 configured in accordance with the prior art. The panel 100 includes a frame 106 and a plurality of stringers 104 attached to a skin 102. The stringers 104 are “hat-section” stringers having a raised portion 103 and opposing flange portions 105. The flange portions 105 are attached directly to the skin 102.
The frame 106 includes a base portion 109 and an upstanding portion 110. The upstanding portion 110 includes a plurality of mouse holes 114 through which the raised portions 103 of the stringers 104 extend. The base portion 109 is attached to the stringer flange portions 105 and the skin 102. The base portion 109 includes a plurality of steps or “joggles” 112 positioned just outboard of the stringer flange portions 105. The joggles 112 allow the base portion 109 to step off the stringer flange portions 105 and onto the skin 102. This allows the base portion 109 to be fastened directly to the skin 102 between the stringers 104 without causing gaps or excessive preload between the base portion 109 and the skin 102.
One shortcoming of the prior art panel 100 is the manufacturing cost. Forming the joggles 112 in the frame 106, for example, adds additional cost when compared to a similar frame without joggles. This is especially true if the frame 106 is manufactured from composite materials rather than metal, because forming joggles in composite materials typically requires special tooling and/or a post-cure machining process.